1. Field of the Invention
The present invention relates to a petroleum water heater and, more particularly, to a liquid hydrocarbon fuel combustor to be used with the water heater or the like.
2. Description of the Prior Art
As burning means for burning a liquid hydrocarbon fuel, there has been available in the prior art what is called a "gun-type burner". This burner ignites a mixture of air, which is blown from a blower motor, and kerosene droplets, which are pressurized by an electromagnetic pump and atomized by a nozzle, by a high-voltage discharge thereby to burn that mixture. Nevertheless, the gun-type burner generally has a high ratio of excess air so that it has an accordingly low heat efficiency. Because of the yellow or yellowish-orange flame combustion, moreover, carbon left unburned deposits on the inner wall of the can-type body of the burner thereby to deteriorate the initial efficiency, and the resultant burning noises are large. From the standpoint of economy of energy and resources, therefore, there arises a requirement for improving the efficiency, or, from the standpoint of prevention of noises to the neighbourhood in urban lives, there arises a requirement for dropping the sound level of the noises. In order to meet those requirements, there has been developed a combustion system such as a rotary gas burner or a heater evaporation system, in which kerosene droplets are gasified to ensure the blue flame combustion. However, the former system has a defect that an offensive order is emitted as a result of the incomplete gasification of the kerosene during the time period from the ignition to the instant when the flame become stable and at the time when the flame is quenched. On the other hand, the latter system is inconvenient, when used, in that the combustion cannot be instantly started because of necessity for a time period for preheating the heater, and has a difficulty that a control mechanism such as a mechanism for controlling the temperature of the heater has a complicated construction. Both the systems are basically improved in that the kerosene droplets are gasified but they are so complicated as to require special skills when they are maintained and are to be inspected. The present invention is directed to what is called a "recirculation system", as is different from those systems according to the prior art. The recirculation system is known in the art as one of countermeasures for reducing emission of nitrogen oxides NO.sub.x from boilers for business use. According to the recirculation system, the flame is changed into a blue one by the use of a remarkably large-scale apparatus for recirculating a portion of the combustion gas to the back of a fuel atomizing nozzle thereby to control the content of the NO.sub.x in the combustion gas. The application of that recirculation system as it is to a domestic petroleum water heater or the like has invited with difficulty the problems that the burning noises are large and that the running cost is high.